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  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

December Events – a brilliant crescent Venus, Jupiter, and moon-drenched meteors

Venus – brilliant shortly after sunset to southwest

Chart shows position of Venus, roughly two fists (18 degrees) above the southwest horizon for much of December. During the last half of the month it will move closer to the Sun - and thus closer to the horizon half an hour after Sunset and by the end of the month will only be about 8 degrees high.  Vega and Altair will be much dimmer, but should show within about 45 minutes after sunset. (Created from Starry Nights Pro screen shot.)

Chart shows position of Venus, roughly two fists (18 degrees) above the southwest horizon, for much of December. During the last half of the month it will move closer to the Sun – and thus closer to the horizon half an hour after sunset and by the end of the month will only be about 8 degrees high. Vega and Altair will be much dimmer, but should show within about 45 minutes after sunset. (Created from Starry Nights Pro screen shot.)

For telescope users – and maybe even those with binoculars – Venus does a gorgeous job of showing off its phases this month as it shrinks and grows at the same time.  For all of us, with telescope or not, it’s a brilliant “evening star” dominating the southwestern sky about half an hour after sunset.

Galileo was the first to see this and it was part of his argument for a Sun-centered solar system. Like Galileo, if you really want to see the phases you need a telescope, though near the end of the month you may be able to detect its thin crescent with good binoculars held very steady.

You won’t have any trouble finding it.  It’s that most brilliant “star” about 18 degrees – a little less than  two fists held at arm’s length – above the southwestern horizon half an hour after sunset.  It shrinks in terms of the amount of its disc that is lit. At the start of December 2013 about one third of the disc is lit – by the end of the month this will drop to just 5 percent. Amazingly, it stays almost the same brightness all month – in fact, this is the time it is at its most brilliant. Why? Because it is overtaking Earth in its orbit and in January will pass between us and the Sun – a sort of “new moon” phase, then become visible in the morning sky. ( When Venus is in its “full moon” phase it is farthest from us, so even though nearly the entire disc is lit, it does not appear nearly as bright.)

Positions of inner planets in mid-December, 2013. All are moving counter clockwise and Venus is about to overtake the Earth, passing between us and the Sun.

Positions of inner planets in mid-December, 2013. All are moving counter clockwise and Venus is about to overtake the Earth, passing between us and the Sun. Mars is positioned to be seen in our morning sky and Mercury is visible at the start of the month before dawn, but is pretty much lost most of the month in the glare of the Sun.

And about the growing Venus? Well, as it gets nearer to us it also appears larger. At the start of the month it’s disc about 38 seconds in diameter – by  the end of the month it is nearly a full minute of arc in diameter. To give you an idea what a minute of arc is, stand on the goal line of a football field and have a friend go down to the 10 yard line at the othe end and hold up a quarter? Can you see it? You may be able to if you have excellent vision.

On the other hand, a quarter held nine feet away is roughly the size of the full Moon – or Sun – in our sky – about 30 minutes of arc, or 30 times larger than Venus will appear in a telescope at the end of the month.

If you do go looking for the Venus crescent with binoculars or a small telescope, go out early. Locate  it while still in twilight, about half an hour after sunset. There’s less glare then and so it is easier to see the form. Later, as it gets fully dark, Venus is so bright you may find detecting its crescent difficult even in a telescope.

Jupiter – very bright as it rises in the east a couple hours after sunset

Click image for larger version. Prepared from Starry Nights Pro screen shot.

Click image for larger version. Prepared from Starry Nights Pro screen shot.

So is Venus the only special show in in our December skies this year? No. If you wait until “prime time” – about 8 pm – you will see a very bright “star” rising in the east. This is Jupiter, which by the end of the month starts coming up right after sunset.  Once it’s fairly high in the sky it makes a good target for binoculars. Its disc won’t be quite as large as Venus, but it does have four bright Moons and you can almost always find one or two of them with binoculars – sometimes three or even four.  Galileo did it four hundred years ago with a telescope that certainly wasn’t as good as most modern binoculars, but was a bit more powerful. Again, you need to hold your binoculars steady and focus them carefully.

Geminids – nice, but they will be drowned out some by moonlight

We also have the best meteor shower of the year putting in its annual appearance in December – the Geminids. Unfortunaetly, this year it will have to compete with the nearly full Moon. Still, Geminid meteors tend to be slow and quite bright, so even with the Moon you should see some. The shower is forecast to peak just after midnight (EDT) on Saturday morning, December 14th. That means late on the night of December 13th – hmmm, Friday, the thirteenth – should be good for seeing Geminids and the best views  will come in the very early morning hours of Saturday when the Moon is low in the west and the shower’s radiant point – in Gemini near Jupiter – is high in the sky.

Solstice – December 21, a good reason to celebrate

You need not be a Druid to celebrate this just after midnight EDT on December 21, 2013.  For northern hemisphere observers the winter solstice means the Sun has stopped running south and is turning around and heading back north. Of course it will take a few months before it’s warming rays change our weather much, but the fact that it is heading back north is a good sign.

It’s hard to imagine just how much that would mean to people living off the land and dependent on the seasons. Even in my warm home I am  cheered by the change, Every morning when I take the dogs out I see the Sun rising on the southeast horizon. At this time of year it appears to stand still for a week or so – but by the end of the month the northward movement becomes noticeable as I mark its path by the trunks of the bare trees I see it through. Of course for those of you in the southern hemisphere this marks the start of summer.

Christmas Star – it’s in your heart, but either Venus or Jupiter will be a nice reminder

In December I frequently get asked about the Christmas Star and while competing scientific theories have abounded about it for centuries, in the final analysis it is a Christmas myth that you can choose to believe, or not believe. Various scientific explanations – informed guesses – range from certain gatherings of planets, to a comet or super nova. Part of the problem is we don’t know the date – not even the year – Jesus of Nazareth was born, so various astronomical  – and astrological – possibilities exist depending on the date chosen. Me, I just take any bright star that’s visible and treat it as  a symbolic Christmas Star. This year we have Venus in the west for a couple hours after sunset – and by the time it sets we have a very bright Jupiter rising in the east.

Your Venus assignment . . .

. . . should you accept it, is – observe seven weeks of Venus with a special treat February 27th!

The position of the moon, Venus, and the Sun just after sunset as shown in Stellarium software.

The position of the moon, Venus, and the Sun just after sunset as shown in Stellarium software.

With naked eye:

  • Watch Venus at least once a week for the next seven weeks just after Sunset.
  • Make a drawing showing it’s changing position each week.
  • Check your drawing against the actual positions of Venus and the Earth as they circle our star, the Sun.

Ponder: Why do you see what you see? That is, think about the actual positions of your spacestation (Earth), Venus, and the Sun and relate that to what you see in the sky. This is an excellent opportunity to develop an intuitive sense of the two realities we face – the reality of what we see in our sky and the scientific reality of how ourplamet – and the others are moving about a star.

With binoculars:

  • Do the naked eye observation above
  • Use binoculars to look for any sign that Venus is beginning to show something of a crescent. Or for that matter, any sign of  it going through any phase.  This is a challenge and it is important that you do this as soon after sunset as you can see Venus – then it will be at its highest point in your sky and the background will not provide too much contrast, since it will still be twilight. Draw what you see and note the date. It will change as the weeks wear on.

(Yes, you can see Venus in the day time with binoculars – and sometimes with your naked eye – but I don’t like to encourage looking for objects near the Sun – too much danger of accidentally looking at the Sun and that will damage your eyes – very bad. So wait for the Sun to set – but observe immediately afterwards.)

Ponder: Again, why do you see what you see? That is, think about the actual positions of your spacestation (Earth), Venus, and the Sun and relate that to what you see with your binoculars in terms of the phases of Venus.

With telescope (any size):

Galileo was using about 20X with a terribly small and poor objective lens. Any modern instrument of any size will be better! So you can certainly see what he saw – and should be able to figure out what he figured out, especially since you already know what he believed, but needed to prove – that the planets go around the Sun.

  • Do the naked eye assignment above.
  • With your telescope observe Venus as soon after sunset that it is visible. When I looked for it February 1 it popped into plain, naked-eye view three minutes after Sunset. (Yes, you can see Venus in the day time with a telescope – and sometimes with your naked eye – but I don’t like to encourage looking for objects near the Sun – too much danger of accidentally looking at the Sun and that will damage your eyes – very bad. So wait for the Sun to set – but observe immediately afterwards.)
  • Use the same telescope and same eyepiece each time you observe and note the size of Venus as best you can. (Ideally you would use an eyepiece with a reticle that allowed you to actually measure the size.)
  • Note the phase of Venus and make a quick drawing to indicate it.  Be sure to date your observations.

Ponder: Again, why do you see what you see? That is, think about the actual positions of your spacestation (Earth), Venus, and the Sun and relate that to what you see with your telescope  in terms of the changing size and  phases of Venus.

Resources for naked eye, as well as binocular and telescope observation:

It’s good practice to use the altitude/azimuth system, however.  The first number in the sequence below is the azimuth – that is the compass bearing. In this syetm south is 180, southwest, 225, and west 270.  Altitude is degrees above the horizon. Remember, your fist with arm extended covers roughly 10 degrees.

Here are the azimuth and altitude coordinates for Venus for the Friday of each week during the next two months. These are for my location at nearly 42-degrees North latuitude, though are a reasonable approximation for folks near this latitude. For others, I suggest you consult Stellarium or similar software.

These are the position just after local Sunset.

2/6 233, 38
2/13 241, 37
2/20 248, 35
2/27 256, 31

This last date is special. Venus will appear to be cradled in the arms of a crescent moon, barely 3 days old – or nearly so – what you see will depend on your location, but both the moon and Venus should fit nicely in the same binocular field.

3/6 263, 26
3/13 271, 18

At this point you need a really clear western horizon. By the 20th it will be just one fist – 10 degrees – above that horizon and difficult to spot.

3/20 278, 9

March 20th or 21st is about the last day I expect to easily see Venus during this sequence. I just don’t like playing games with the Sun and it is getting too close and too low.  By the next Friday – the 27th – it sets just 10 minutes after the Sun. Near that date I plan to go to where the ocean is my western horizon.

Actually in the couple days before March 27 you may find it easier to catch it in the morning sky. On the 27 – when it is between us and the Sun – it rises more than half an hour before the Sun in the Northeast at Azimuth 75 – again, be careful and be aware of Sunrise in your location. You don’t want to be looking at Venus in binoculars or a telescope and instead catch the rising Sun. Any glimpse at the Sun through an unfiltered optical instrument can seriously damage your eyes. But you can follow the crescent show in reverse after this if you are an early riser. We see Venus  in both our morning and evening skybecause Venus is north of the Sun. For example, on Macrh 27 the Azimuth of the Sun at Sunrise is 84 degrees, the azimuth of Venus is 75. (Yes – yes – spring is that close! )

Background

Ptolemy

Ptolemy

For Galileo, the view that Venus showed phases like the moon was a good proof that the Copernican theory was correct – the planets all revolved aorund the Sun. Ptolemy was wrong.

I used to accept that as obvious, for it’s pretty easy to see how our view of Venus would cause it to go through phases. However, think about the Ptolemaic system a little with the Earth at the center and suddenly the water gets a bit muddy. I mean, if the moon shows phases while going around the Earth, why wouldn’t Venus? And as I started to think about that it occurred to me that Venus does not APPEAR to go around the Earth. Whoa!

We see it in the morning sky in the east  and we see it in the evening sky in the west – but we never see it move from east to west as every other star does, including our Sun. So it does not appear to go around the Earth – yet the Ptolemaic system said it did.

Make sense? Not to me.  The Ptolemaic system puts the Earth at the center, then the Moon, Mercury, Venus, the Sun, etc.  But we don’t see Venus ( or Mercury) go across our sky. The ancients would not have seen the phases – that needed a telescope – but they certainly knew Venus and Mercury only appeared in the East or the West – never over head. Why?

In trying to understand the answer to that question I learned a lot more about the Ptolemaic system than I ever knew and I gained a much deeper understanding of why the news Galileo brought with his telescope 400 years ago was so disturbing to so many people – they had such a perfect universe where everything made sense and fit into a nice tidy concept.

Well, the concept as Aristotle developed it was nice and tidy. But it didn’t always match observation. It took Ptiolemy to come up with a scheme that would account for Venus and Mercury being only in the eastern or western sky. It was his epicycles that held the key. If you want to understand it, I suggest you read this. You migth also go to this Web page and scroll down to the section on the observations of Venus – there’s a helpful animation there as well.

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